title: Vav1-mediated scaffolding interactions stabilize SLP-76 microclusters and contribute to antigen-dependent T cell responses.
abstract: The guanine nucleotide exchange factor (GEF) Vav1 synergizes with the adaptor protein SLP-76 (Src homology 2 domain--containing leukocyte phosphoprotein of 76 kD) to support T cell development and activation. In response to ligation of the T cell receptor (TCR), SLP-76 is assembled into microclusters that provide an essential platform for the signaling events that drive T cell activation. We found that Vav1 selectively entered SLP-76 microclusters, rather than TCR microclusters, influencing their stability and function. The carboxyl terminus of Vav1, which consists of Src homology domains, was both necessary and sufficient for the entry of Vav1 into SLP-76 microclusters; however, this fragment of Vav1 was insufficient to stabilize the microclusters, and it potently suppressed T cell activation. This indicated that the amino terminus of Vav1, which has the GEF domain, also contributed to the integrity of SLP-76 microclusters and thereby to T cell activation. These microcluster-stabilizing functions were independent of the GEF activity in the amino terminus of Vav1 and were unaffected if the GEF function of Vav1 was either inactivated or constitutively activated by mutation. In contrast, Vav1 deletion mutants lacking either the calponin homology domain or the catalytic core of the GEF exhibited mild scaffolding defects, but they differentially affected TCR-dependent calcium ion (Ca²+) responses. We conclude that multiple GEF-independent scaffolding functions distributed throughout the amino terminus of Vav1 contribute to the activation of T cells by acting synergistically to increase the stability and function of SLP-76 microclusters.
authors.affiliation: Program in Immunology, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, MA 02111, USA.
authors.forename: Nicholas R
authors.initials: NR
authors.lastname: Sylvain
authors.forename: Ken
authors.initials: K
authors.lastname: Nguyen
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Bunnell
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D015703:Antigens, CD / Q000378:metabolism; D000945:Antigens, Differentiation, T-Lymphocyte / Q000378:metabolism; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D047468:Immunoprecipitation; D019169:Jurkat Cells; D007734:Kymography; D037181:Lectins, C-Type / Q000378:metabolism; D008213:Lymphocyte Activation / Q000235:genetics / Q000502:physiology*; D008954:Models, Biological; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D051567:Proto-Oncogene Proteins c-vav / Q000235:genetics / Q000378:metabolism*; D013601:T-Lymphocytes / Q000378:metabolism*; D000099192:CD69 Antigens
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D002118:Calcium; D037181:Lectins, C-Type; D010750:Phosphoproteins; D051567:Proto-Oncogene Proteins c-vav; D000099192:CD69 Antigens; C092947:SLP-76 signal Transducing adaptor proteins; C496618:VAV1 protein, human